U.S. patent number 5,022,674 [Application Number 07/505,289] was granted by the patent office on 1991-06-11 for dual pyrotechnic hybrid inflator.
This patent grant is currently assigned to Bendix Atlantic Inflator Company. Invention is credited to Teresa Bazel, Robert J. Bishop, Roy Brown, Richard L. Frantom, Robert Kremer, Klaus Ocker, Donald Renfroe, James Rose.
United States Patent |
5,022,674 |
Frantom , et al. |
June 11, 1991 |
Dual pyrotechnic hybrid inflator
Abstract
An inflator for an air cushion including a pressure vessel
comprising a hollow sleeve for storing a quantity of inert gas such
as Argon. One end of the sleeve is closed by a first pyrotechnic
actuator assembly while the other end of the sleeve may include a
closed end or another pyrotechnic actuator assembly. The pressure
vessel is secured within a diffuser which directs inflation gases
into the air cushion. The pressure vessel in cooperation with the
diffuser defines various regions which assist in reducing the gas
turbulence and heat transfer between the gas and the diffuser.
Inventors: |
Frantom; Richard L. (Richmond,
MI), Bishop; Robert J. (Washington, MI), Kremer;
Robert (Fraser, MI), Ocker; Klaus (Fraser, MI),
Brown; Roy (Hot Springs, AR), Rose; James (Fairfax,
VA), Renfroe; Donald (Haymarket, VA), Bazel; Teresa
(Annandale, VA) |
Assignee: |
Bendix Atlantic Inflator
Company (Troy, MI)
|
Family
ID: |
24009715 |
Appl.
No.: |
07/505,289 |
Filed: |
April 5, 1990 |
Current U.S.
Class: |
280/741;
280/737 |
Current CPC
Class: |
B60R
21/272 (20130101); B60R 2021/2633 (20130101) |
Current International
Class: |
B60R
21/26 (20060101); B60R 021/26 () |
Field of
Search: |
;280/737,741 ;222/5
;423/262 ;102/202,202.5,202.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Bertsch; Richard A.
Claims
We claim:
1. An inflator for an air cushion or bag comprising:
a hollow, cylindrical sleeve having first and second ends;
first means for enclosing the first end of the sleeve;
second means for enclosing the second end (28) of the sleeve, the
sleeve, and first and second means comprising a pressure vessel for
storing a quantity of pressurized inert gas used to inflate the air
bag;
the first means comprises an initiator housing assembly comprising
a manifold adapted to be secured to the sleeve at the first end
including a flat edge first orifice, a first frangible member
comprising a first rupturable disk secured about the first orifice,
wherein one side of the disk is exposed to the stored gas; the
manifold further including first flow control means, positioned
remote from the pressure vessel for regulating the flow of
inflation gas as it exits the pressure vessel and a pyrotechnic
first actuator means for breaking the first frangible member
wherein the initiator housing assembly, includes an initiator
housing secured to the manifold assembly remote from the gas in the
pressure vessel, the initiator housing comprises a hollow,
necked-down portion, the first actuator means is removably received
in the housing and closely spaced to the disk so that upon
activation of the pyrotechnic actuator means the disk is ruptured
by a shock wave to initiate flow of the inflation gas through the
first orifice and first flow control means.
2. The inflator as defined in claim 1 wherein the initiator housing
assembly includes first screen means for filtering solid matter in
the inflation gas prior to the gas exiting the first flow control
means; the screen means secured to the manifold assembly downstream
of the disk and upstream of the first flow control means.
3. The inflator as defined in claim 2 wherein the second means
includes a second manifold assembly connected to the sleeve to form
part of the pressure vessel and positioned about the generator
housing, wherein the second manifold assembly includes a flat edge
second orifice closed by a second frangible member comprising a
second rupturable disk positioned apart from the second housing
end, second flow means for regulating gas flow therethrough.
4. The inflator as defined in claim 3 wherein the first and second
flow means comprise first and second flow orifices respectfully,
and wherein the flow area of the first flow means is less than the
flow area of the second flow means.
5. An inflator for an air cushion or bag comprising:
a hollow, cylindrical sleeve having first and second ends;
first means for enclosing the first end of the sleeve;
second means for enclosing the second end (28) of the sleeve, the
sleeve, and first and second means comprising a pressure vessel for
storing a quantity of pressurized inert gas used to inflate the air
bag;
the first means comprises an initiator housing assembly comprising
a manifold adapted to be secured to the sleeve at the first end
including a flat edge first orifice, a first frangible member
comprising a first rupturable disk secured about the first orifice,
wherein one side of the disk is exposed to the stored gas; the
manifold further including first flow control means, positioned
remote from the pressure vessel for regulating the flow of
inflation gas as it exits the pressure vessel and a pyrotechnic
first actuator means for breaking the first frangible member
wherein the second means comprises a generator housing assembly
including a hollow, elongated generator housing including a first
housing end and a second housing end, the first housing end is
secured to the second end of the sleeve, the second housing end
(86) includes at least one opening enclosed by a second frangible
member comprising a second rupturable disk.
6. The inflator as defined in claim 5 wherein generator housing
assembly further includes a grain trap, including a plurality of
trap openings, positioned proximate the second housing end, a
quantity of formed propellant and a resilient member for biasing
the propellant into the grain trap and a pyrotechnic second
actuator means spaced from the resilient member for initiating,
upon activation, the burning of the propellant.
7. The inflator as defined in claim 6 wherein the second actuator
means includes a divergent nozzle spaced from and facing the
propellant.
8. The inflator as defined in claim 7 wherein the second actuator
means includes an ignition enhancing means for rapidly initiating
burning of the propellant in the divergent nozzle.
9. The inflator as defined in claim 7 wherein the ignition
enhancing means includes a quantity of boron potassium nitrate.
10. The inflator as defined in claim 5 wherein the actuator housing
assembly and generator housing assembly are welded to the sleeve in
a manner to permit the unobstructed migration of stored gas to the
point of weld.
11. The inflator as defined in claim 10 wherein the first actuator
means, second actuator means and propellant are located exterior to
the stored gas.
12. The inflator as defined in claim 11 wherein the generator
housing includes a first housing end and a second housing end, the
first housing end is secured to the second manifold assembly, the
second housing end includes at least one opening positioned
opposite the second rupturable member such as a disk.
13. The inflator as defined in claim 12 wherein a second screen is
positioned about at least one opening in the second housing end and
mated with a portion of the second manifold assembly.
14. An inflator for an air cushion or bag comprising:
a hollow, cylindrical sleeve having first and second ends;
first means for enclosing the first end of the sleeve;
second means for enclosing the second end (28) of the sleeve, the
sleeve, and first and second means comprising a pressure vessel for
storing a quantity of pressurized inert gas used to inflate the air
bag;
the first means comprises an initiator housing assembly comprising
a manifold adapted to be secured to the sleeve at the first end
including a flat edge first orifice, a first frangible member
comprising a first rupturable disk secured about the first orifice,
wherein one side of the disk is exposed to the stored gas; the
manifold further including first flow control means, positioned
remote from the pressure vessel for regulating the flow of
inflation gas as it exits the pressure vessel and a pyrotechnic
first actuator means for breaking the first frangible member
including diffuser means in communication with the first flow
control means, for supporting the pressure vessel and for directing
inflation gas into an air cushion, the diffuser including a lower
portion adapted to support a lower portion of the pressure vessel,
the diffusing further including an upper portion adapted to mate
along with an upper portion of the pressure vessel, the diffuser
upper portion including a plurality of openings to permit inflation
gas to flow thereacross, and defining in cooperation with the
pressure vessel two volume regions proximate the upper portion of
the pressure vessel so as to provide a means for reducing
turbulance of the inflation gas and to reduce the heat transfer of
the inflation gas with the diffuser.
15. The inflator as defined in claim 14 wherein the diffuser
includes end caps, one cap attached to the actuator housing
assembly and the other cap attached to the generator housing
assembly for enclosing respective ends of a main portion of the
diffuser.
16. The inflator as defined in claim 14 wherein the lower portion
of the diffuser includes a trough, enclosed by a portion of the
pressure vessel, adapted to receive wires associated with the first
actuator means and for shielding these wires from the inflation
gas.
17. The inflator as defined in claim 14 wherein the diffuser means
comprises attachment means comprising a plurality of bolts
extending therefrom for containing the air bag and for providing
means for directly attaching the diffuser to vehicle support
structure.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a device for inflating an air
cushion, air bag, or the like.
Inflatable bag restraint systems have been shown to reduce the
seriousness of injuries and number of fatalities resulting in motor
vehicle accidents. There exists a number of means for inflating an
air cushion or air bag such as utilizing a quantity of stored gas
which is selectively released to expand the air bag. Alternatively,
a gas source derived from a gas generating material propellant such
as sodium azide, which upon ignition thereof generates a sufficient
quantity of gas to expand the air bag. The third type of gas source
results from a combination of the stored compressed gas and a gas
generating or enhancing material. This last device is often
referred to as an augmented gas or hybrid inflator. Various hybrid
inflators have been shown in the past such as those illustrated in
U.S. Pat. Nos. 3,756,621 and 3,895,821. The inflator shown in U.S.
Pat. No. 3,756,621 uses a separate squib or initiator to ignite the
propellant and an actuator to open an exit passage to initiate
compressed gas flow. U.S. Pat. No. 3,895,821 mounted a single squib
outside the pressurized environment of the pressure vessel to
ignite the propellant. In that invention a single squib and
propellant chamber or housing is placed in a compressed inert gas
environment. Upon initiation of the propellant, a heated media is
generated, comprising hot gas and particulates which are directed
by a discharge nozzle into a small mixing cavity or chamber
adjacent a rupturable disk causing same to burst, initiaing gas
flow into an air bag. Hot gases continue to be emitted from the
propellant chamber and mix with the cold pressurized gas in a small
mixing chamber before continuing into the bag to inflate same. The
present invention yields advantages in relation to the prior art in
that the number of leak passages are reduced, electrical leads are
shielded from the harsh environment of the inflation gases, and the
inflation rate is controlled.
It is an object of the present invention to provide a hybrid
inflator which can rapidly and efficiently generate a sufficient
quantity of gas to inflate a cushion or air bag during a vehicle
crash situation. A further object of the present invention is to
provide an inflator for an air cushion or air bag which improves
upon the deficiencies of the prior art.
Accordingly the invention comprises: a hybrid inflator for an
cushion comprising in one embodiment a hollow, cylindrical sleeve
enclosed at both ends by pyrotechnic actuator assemblies. The
enclosed sleeve comprises a pressure vessel for the storage of a
quantity of pressurized inert gas such as Argon. A trace amount of
helium may be present to facilitate leak testing of the pressure
vessel. The first actuator assembly comprises an actuator,
detonator or squib for generating a shock wave to break a frangible
disk member to enable gas flow through flow orifices associated
with the first actuator assembly. A second actuator assembly is
positioned opposite from the first actuator assembly and includes
another detonator, initiator, squib or the like for initiating the
burning of a quantity of propellant. The propellant elevates the
temperature of the stored inert gas to increase its volume prior to
inflating the air cushion. In one embodiment of the invention a
second frangible disk, forming part of the pressure vessel, is
positioned opposite the propellant and upon being broken permits
heat generated by the propellant to enter the pressure vessel. In
another embodiment of the invention, upon breaking the second disk
a second flow path is created to permit the egress of the heated
inflation gas out from the pressure vessel. In an embodiment of the
invention, only a single actuator assembly is used which upon the
breakage of the frangible disk permits the stored gas to flow out
of the pressure vessel in a direction generally about the
propellant. The invention additionally includes a diffuser which
supports the inflator and provides a flow passage to the air
cushion. The diffuser also supports the air cushion. The diffuser
envelopes the inflator in a manner to create relatively large
volume regions downstream of any gas outlet in the pressure vessel.
This design reduces gas turbulence and reduces the amount of heat
transfer between the heated inflation gas and the diffuser.
Many other objects and purposes of the invention will be clear from
the following detailed description of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 illustrates a front cross-sectional view of the present
invention.
FIG. 2 illustrates a side end view the present invention.
FIG. 3 illustrates an alternate embodiment of the generator housing
assembly.
FIG. 4 shows a cross-sectional view of the propellant used.
FIG. 5 is an enlarged view of an exemplary weld joint.
FIG. 6 is a partial, projected view of a diffuser.
FIG. 7 illustrates prior art diffuser.
FIG. 8 is a side view of the diffuser with a folded air bag.
FIG. 9 is a diagramatical view of an air bag.
FIG. 10 illustrates an alternate construction of a portion of the
present invention.
FIG. 11 illustrates a graph of inflation curves.
FIG. 12 illustrates an alternate embodiment of the present
invention.
FIG. 13 illustrates a further embodiment of the present
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
With reference to FIG. 1, there is shown a hybrid inflator 10 for
inflating an air cushion such as an air bag usable within a vehicle
occupant restraint safety system. The inflator 10 comprises a
pressure tank generally shown as 20 which includes a hollow sleeve
22. The pressure tank 20 in the space 24 is filled and pressurized
with an inert gas such as Argon. The gas may also be a mixture of
Argon and another inert gas such as helium. It is contemplated that
the amount of helium be approximately 2% by volume of the Argon
gas. The purpose of using the second inert gas is to provide a
means for detecting defects in the various weld joints of the
hybrid inflator which would cause leakage. Devices for sensing the
presence of helium such as mass spectrometers are well known in the
art. The pressure vessel, and more particularly the sleeve 22, is
enclosed at its respective ends 26 and 28 by an initiator housing
assembly 30 and by a generator housing assembly 80, which may be
viewed as part of the pressure vessel 20.
The initiator housing assembly 30 includes an initiator housing 32
comprising a necked down, narrowed portion 34 and a wider end
portion 36. Threadably inserted within the narrowed portion 34 is a
spacer or housing 38 having a central opening 39 to receive a
detonator 40 of known construction. Extending from the detonator
are actuation leads or wires 42. An O-ring 44, provides a seal
between the detonator 40 and the spacer 38.
Attached to the initiator housing 32, forming part of the assembly
30, is a manifold assembly 50. The manifold assembly comprises an
outer cylindrical portion 52, attached such as by welding (see
numeral 54), to the initiator housing 32. The manifold assembly 50
further includes a smaller diameter cylindrical portion 56 recessed
relative to the outer portion 52, which is adapted to mate with and
receive one end 26 of the sleeve 22. The sleeve 22 and manifold
assembly 50 are attached such as at the circumferential weld 58.
The manifold assembly further includes a large, flat edge orifice
60 enclosed by a frangible member such as a burst disk 62. A
suitable burst disk 62 may be fabricated of nickel or stainless
steel. The burst disk is attached to the manifold assembly 50 at a
circumferential plasma weld 63 facing the pressurized gas.
Press fit against the wall of the smaller diameter portion 56 is an
apertured screen 64 comprising a plurality of openings 66,
positioned about a central opening 68, coaxial with the center of
the detonator 40. Upon assembly, the screen 64 is slightly deformed
inwardly by the narrow portion 34 of the initiator housing 32 to
prevent rattling. The screen 64 prevents large objects such as
portions of the disk 62 from entering the air bag. The outer
cYlindrical portion 52 of the manifold assembly 50 includes at
least two orifices 70a and b, diametrically opposed, to provide for
a neutral thrust, wherein the total flow area of the orifices 70a
and 70b is significantly smaller than the area of the opening 60.
Upon actuation of the detonator 40 a pressure, a shock wave is
created to break the frangible member or disk 62 permitting at
least stored inflation gas to exit the pressure vessel 20. This
initial inflation is sometimes referred to as a cold inflation.
In the present invention the narrow orifices 70a and b regulate the
flow rate of the inflation gas exiting the pressure vessel 20. The
orifice 60 about which the burst disk 62 is positioned does not
generate any substantial pressure drop due to its large size. This
construction yields the advantage of standardization of design of
the inflator from one sized model to The burst disk 62 to orifice
70a and 70b diameter relationship establishes the rupture point of
the burst disk 62 as a safety relief device or valve in the event
of an over pressurization of the pressure vessel resulting from
overheating or flattening of the pressure vessel due to misuse.
The gas generator housing assembly 80 comprises a stepped housing
82 having an enlarged end 84 mating with the other end 28 of the
sleeve 22 of the pressure tank 20. The sleeve 22 and housing 82 are
joined at a circumferential weld 87. The housing 82, at its inner
end 86, includes a central opening 88, covered by a thin burst disk
90 typically fabricated of stainless steel. The disk 90 is welded
to the housing 82 in a manner as discussed above.
FIG. 3 illustrates an alternate embodiment of the generator housing
assembly 80 in which the end 86, at the previous location of the
opening 88, includes a plurality of smaller openings 92, covered by
the burst disk 90. In this embodiment the housing 82 material,
between the openings 92, provides additional support for the burst
disk 90, permitting same to be made significantly thinner than the
burst disk 90 shown in FIG. 1. A typical thickness of the burst
disk 90 in this situation would be 0.1 mm (stainless steel).
Returning to FIG. 1, positioned within the hollow interior of the
housing 82 is a grain trap 94 having a plurality of openings 96
therein, which prevent extrusion of the burning propellant 100 into
the openings 96. Upstream of the grain trap is a quantity of
extruded or shaped propellant 100. The propellant 100 may be Arcite
such as that disclosed in U.S. Pat. No. 3,723,205, which is
incorporated herein by reference.
The propellant 100 is biased against the grain trap 94 by a wave
washer 102. The thickness of this resilient member, i.e., wave
washer 102, may be varied to accommodate varying lengths of
propellant 100. Threadably received within the housing 82 is a
housing 104 of having a central opening 106 which terminates at one
end thereof in a conical, divergent nozzle 108. Received within the
opening 106 is another detonator or initiator 110 of known design,
having a plurality of electrical leads 112 attached thereto. Within
the divergent nozzle 108 is an ignition enhancing material 109
comprising boron potassium nitrate whose flame temperature and
quantity are suitable for instanteously igniting the propellant
100.
With reference to FIG. 4, this figure illustrates a cross-sectional
view of the propellant 100. The exterior 120 of the propellant 100
is formed in a cloverleaf-type pattern with each cloverleaf having
a central opening 122. The purpose of this construction is to
provide for a relatively constant propellant burn rate. As the
propellant 100 burns its exposed area remains generally constant,
that is, as the exterior of the propellant burns its outer surface
area reduces while the surface area about each of the cylindrical
openings 122 increases, yielding a uniform burn surface and a
resulting controllable burn rate. The burn rate is further
controlled by the flow area of the central openings 92 or 88. As
can be seen, the pressure in the generator housing 82 (which
contains the propellant 100) as determined by the openings 92 or 88
is also effective in controlling the total propellant burn
time.
The inflator 10 further includes a diffuser 130 comprising end caps
132 and 134, and a main portion 140. The shape of each end cap can
be seen in FIG. 2. The end caps 132 and 134 are secured
respectively to the initiator housing 32 and gas generator housing
80. This securement may be accomplished by providing the gas
generator housing 82 with a plurality of extensions or serrations
150, which extend through openings 152 in the end cap such as 134.
These extensions 150 during assembly are crimped over, holding the
end cap 134, diffuser 130 and pressure vessel 20 in place. The
other end cap 132 may be secured to the initiator housing 32
through a like plurality of extensions or serrations 156 received
through openings 158 in the end cap.
The gas generator housing assembly 80, or alternatively, the
initiator housing assembly 30, may further include provision for a
fill tube 160 of normal construction through which the inert gases
are communicated to the interior 24 of the pressure vessel 20. Upon
filling the pressure vessel with gas, the fill tube 160 is crimped
at a location such as 162 and sealed at location 163. Subsequent to
the seal weld operation the crimped portion 162 of the tube 160 may
be mechanically squeezed to reopen same to provide for direct
communication of inflation or test gas to the welded or sealed
joint (at location 163).
Reference is made to FIG. 5 which illustrates an exemplary weld
joint such as 58. The following is also applicable to the other
weld joints used within the inflator 10 such as 54 and 87. More
specifically, FIG. 5 illustrates the junction of the left hand end
26 of the sleeve 22 to the manifold assembly 50. During fabrication
of the various assemblies 30 and 80, and after complete fabrication
and filling the inflator 10 with gas, each of the weld joints 58
and 87, are leak tested. To facilitate such testing as well as to
insure the efficacy of each of these weld joints the present
invention contemplates that the various pieces of metal to be
welded will be sized and fit together, prior to such welding, so
that they touch only in the vicinity of the weld generally avoiding
the use of long interference, threaded or press fit contact areas.
As such, FIG. 5 shows that the portion 56 of the manifold 50 is
slightly spaced (see numeral 166) from the sleeve 22. In this
manner, the stored pressurized gas or alternatively a test gas, is
permitted to migrate in a relatively unobstructed manner to the
point of the weld such as 58. By constructing the fit of the
various components in this manner, a leak arising from a defect in
the weld can be readily detected during testing of the pressure
vessel. This construction is in contrast to the prior art which
teaches the use of threadable interconnections or alternatively,
interference and press fit connections. Use of a threaded or press
fit connection impedes the migration of stored or test gas to the
weld point, and as such, leak tests done on prior art inflators did
not always detect a defect in the weld because migration of gas to
the weld point was significantly restricted, i.e., gas could not
migrate to the weld point by the time the pressure vessel was
tested. This deficiency in the prior art resulted in what is called
infant mortality types of failures. Should threaded connections be
required or desired, a milled slot 254 (see FIG. 9) extending the
length of the threads would provide an unrestricted passage of the
gas to the joint under test. FIG. 9 presents an alternative
attachment of parts of the present invention showing a screw thread
connection. There is shown a generator housing 82 having threads
250 received within threads 252 in the end 28 of the sleeve 22. A
milled slot 254 is provided in one of the sets of threads to permit
the direct migration of gas to the weld joint 87. It should be
appreciated that the slot 254 can be in either the housing 82 or
the sleeve 22 of the pressure vessel 20.
FIGS. 2 and 6 illustrate various views of the diffuser 130. FIG. 6,
shows a projected partial view of some of the major components
forming the diffuser. The diffuser 130 is essentially a can of
specific shape designed to cradle and support the pressure vessel
20. As will be seen, the diffuser 130 also supports an air bag. The
diffuser 130 in cooperation with the pressure vessel, also provides
a conduit to communicate the inflation gas to the air bag. The
diffuser 130 shown in FIG. 6 includes the main portion 140 and end
caps 132 and 134 shown in FIG. 1. The main portion 140 may be
fabricated of a lower assembly 180 and an upper assembly 182. The
upper and lower assemblies 182 and 180, respectively, provide for a
three location axial interference fit with the pressure vessel 20.
In cross-section the shape of the diffuser 130 is somewhat
triangular to provide a three-point contact with the pressure
vessel 20. Toward the rear or lower portion as seen in FIG. 6 of
the diffuser its shape generally follows that of the cylindrical
pressure vessel. Toward the front of the diffuser, i.e., in the
direction of the inflating air bag, it departs from the pressure
vessel to define volumes 183a and b. The lower assembly comprises
an open structure having at its lower extreme a longitudinally
extending trough 184. The lower assembly further includes a
plurality of tabs 186 designed to fit through a like plurality of
openings 188 formed in the upper assembly. The tabs 186 may be
bent, crimped or otherwise secured in place. In cross-section the
walls 190a and b taper inwardly to intersect with the circular
pressure vessel 20 at least along a line contact 192a and b. The
walls 190a and b may be arcuately shaped, as shown more clearly in
FIG. 6, to provide an interference fit with a greater area of the
pressure vessel 20. Positioned within the trough 184 and extending
therefrom are a plurality of mounting lugs 204, which may be useful
in mounting the inflator 10 and air bag 202 to cooperating portions
of the vehicle's structure, avoiding the need for and additional
housing (see FIG. 7) to hold the diffuser and inflator, as had been
used in the prior art. Various techniques for attaching the lugs
204 to the lower assembly 180 of the diffuser 130 are known in the
art.
The upper assembly 182 can be formed with a central longitudinally
extending trough 194 which provides at least a point contact (or
contact area) at 196 along the pressure vessel 20. The trough 194
may be arcuately shaped as shown in FIG. 2 to contact a larger area
of the pressure vessel or flat as shown in FIG. 6. The axially
extending trough provides stiffness to the diffuser 130 permitting
lightweight materials to be used. The trough 194 is not essential
to the invention and if eliminated, the front 193 or top as seen in
FIG. 6 of the diffuser would essentially be of planar construction.
The upper assembly 182 may further include a plurality of openings
200 to distribute inflation gas to an air bag 202 which is
positioned thereabout. The orientation of the holes 200 may extend
axially (shown in phantom line) along the top 193 of the assembly
182 or radially or a combination thereof. The location and position
of the holes are chosen to assist in limiting any deformation that
may occur to the diffuser 130 upon generation of the inflating
gases and to evenly distribute the generated gases to the interior
of the cushion or air bag.
An advantage of the increased (dead) volume, i.e., 183a, b and the
use of the openings 200 in top 193 of the diffuser 130 is to
decrease the turbulence in the inflation gas as it exits the
pressure vessel and flows through the diffuser 130. Characteristic
of prior art inflators/diffusers which typically were of circular
cross-section (see FIG. 7), was a high degree of turbulence in the
inflation gas as it exited the pressure vessel. This turbulence
assisted in creating a large heat transfer between the heated
inflation gas and the prior art diffuser. Heat lost from the
inflation gas reduces its volume and hence the efficiency at which
the air bag is inflated. Use of a greater amount of stored gas
and/or propellant was required to compensate for this effect in the
prior art. In contrast, the present invention reduces turbulent
flow, reduces the pressure drop across the diffuser, and reduces
the amount of heat transfer to yield more efficient performance.
FIG. 7 which is illustrative of the prior art, shows a typical
cylindrically shaped inflator 10' positioned within a cylindrical,
closely spaced diffuser 130'. The inflator may be of the hybrid
type such as the present invention or alternatively, a sodium azide
based inflator as is known in the art. Inflation gas exited
openings such as 220 flows turbulently through the diffuser 130' to
inflate an air bag 202 which is diagramatically illustrated. The
diffuser 130', inflator 10' and air bag are typically secured
within a reaction can 222, which is then secured to a portion of
the vehicle such as its instrument panel. Reference is made to
numeral, 224, which illustrates a trapped volume 226 within the
reaction can 222. This volume was not effectively utilized since
the air bag 202 could not be tightly folded therein.
With regard to the present invention, FIG. 8 diagramatically
illustrates an air bag 202 secured about the inflator 10. More
particularly, the air bag 202 comprises an open end 210 into which
is received the diffuser 130 (see FIG. 10). The air bag 202
proximate its end 210 may include a plurality of extending flaps
212a and b, which are received about the diffuser 130 in an
overlapping manner (see FIG. 8) with the mounting lugs 204
extending therethrough. The air bag 202 may be maintained in its
folded configuration by enveloping same with a thin tearable cover
214 shown in dotted line in FIG. 8. This feature allows the unit to
be directly attached to the vehicle mounting structure without the
need for an intermediate housing or reaction can. In this case the
vehicle instrument panel could include a cavity or shape similar to
the reaction can shown in FIG. 7. In contrast, the non-circular
cross-section of the present diffuser 130 relative to the generally
cylindrically shaped inflator 10 or pressure vessel 20 is arranged
to minimize the surface area to which the inflation gases are
exposed and also to minimize the pressure drop to reduce heat loss
without affecting the overall package size of the unit. From FIGS.
1 and 6 it should be appreciated that the exit orifices 70a and b
direct inflation gases directly into the volumes 183a and b of the
diffuser 130. In addition, a further advantage of the present
invention is achieved with regard to the aspect of folding the air
bag and positioning it relative to the diffuser. By utilizing the
generally flat top surface 193 of the diffuser provides an ideal
surface upon which the air bag may be folded.
In view of the above, it is contemplated that the diffuser 130 may
be fabricated of lightweight material. More specifically, the lower
assembly 180 may be fabricated of aluminum, while the upper
assembly 182 may be fabricated of a high strength, low alloy
steel.
Reference is made to FIG. 1 and more particularly to the
orientation of the electrical wires or leads 42 and 112 extending
from the actuator 40 and initiator 110. As can be seen from FIG. 1,
these leads or wires 42 and 112, respectively, are exterior to the
pressure vessel and as such, are not subject to the heat generated
by the actuator 40 or initiator 110 upon excitation. It is
contemplated that the wires 42 will be fed from the right hand side
of the inflator 10 as shown in FIG. 1, through the trough 184 and
exit the initiator at its left side through an opening 220 in the
cover 134. This construction facilitates attachment to a
controller, eliminates loose and dangling wires and reduces the
number of electrical connectors needed. Correspondingly, the
cleanliness of the generated gases in the present invention, are
enhanced as the breakdown of foreign materials (such as due to the
melting of the internal wires) is prevented for better management
of effluent which also reduces toxicological concerns. In the prior
art, such as illustrated by U.S. Pat. No. 3,756,621, the wires
extended through the pressure vessel and were subject to the
extremely harsh environment generated upon activation of propellant
such as 100.
The following briefly describes a typical fabrication process that
may be utilized to assemble and test the inflator 10. The initiator
housing assembly 30 is assembled by positioning the screen 64, if
used, within the manifold assembly 50 and welding the manifold
assembly to the initiator housing 32 at location 54. The burst disk
62 is welded about the opening 60 using a plasma weld process At
this time this sub-assembly does not include the actuator 40 and
spacer 38. The interior of this assembly is evacuated in a test
chamber to create a vacuum, and a test gas such as helium is
exposed to the pressure vessel side of the burst disk 62. A leak
test is accomplished by testing for the migration of helium across
the burst disk weld. It is important to note that helium test gas
will be applied to the side of the burst disk which will tend to
lift it from the surfaces it is welded upon. If test gas is applied
oppositely, the test gas would tend to hold the burst disk to these
surfaces and mask a leak. Thereafter, the sleeve 22 is assembled to
the manifold assembly 50 and welded at 58. The generator housing
assembly 80 is similarly mounted to the sleeve and welded at 87.
Actuation gas comprising Argon and a small percentage of helium, is
placed within the completed pressure vessel 20 and filled to its
operating pressure which is approximately 3,000 psi. Thereafter,
the welds at locations 58 and 87 are leak tested. Subsequently, the
spacer 38 and actuator 40 are threadably received within the
initiator housing 32. The various components comprising the
initiator housing assembly, i.e., the grain trap 94, propellant
100, spring disk 102, housing 104, and initiator 110 are assembled
to the generator housing 82. By following this assembly technique,
if the pressure vessel fails the leak test, the various pyrotechnic
related components need not be scrapped. Further, the present
invention is well suited to a wide range is welding techniques
since the pyrotechnic elements are not mounted during welding. In
the prior art the welding technique was restricted to one which
would generate a minimum heat affected zone so as not to ignite the
mounted pyrotechnic elements. Typically, an electron beam weld was
used, however, this technique is expensive and ill-suited for mass
production. Upon final assembly of the inflator 10, the air bag 202
is secured thereto.
The generator housing assembly is also tested for leaks at the
interface between the burst disk 90 and the generator housing 82 in
a manner described above. The diffuser 130 comprising the end
covers 132 and 134 and the top and bottom assemblies 180 and 182
are thereafter attached to and about the inflator. 10.
The dual pyrotechnic configuration of the present invention yields
flexibility in that the rate of inflation of the air bag 202 can be
controlled. It is desirable to control the initial rate of
inflation so that the air bag does not too forcefully impact the
occupant, especially an out-of-position occupant such as a standing
child. In this regard, the inflator can be made operative by
simultaneously initiating the actuator 40 and the initiator 110.
This type of initiation yields the most aggressive air bag filling
(see Curve A, FIG. 11). Alternatively, the actuator 40 may be
initiated generating a shock wave which ruptures the disk 62,
causing an initial cold gas inflation as the stored Argon inflation
gas exits the flow orificies 70a and b and begins to inflate the
air bag 202 (see Curve B, FIG. 11). Thereafter, for example, after
a time delay 7, 10 or 16 milliseconds, the initiator 110 is
activated thereby causing the propellant 100 to burn, which in turn
raises the temperature of the remaining stored gas within the
pressure vessel, thereby increasing the volume of gas available to
inflate the air bag. In this manner, the initial cold gas inflation
provides for an initially slower inflation rate of the air bag
yielding a relatively soft contact with the out-of-position
occupant, which is thereafter followed by the more rapid inflation
of the air bag upon activation of the initator 110. The sequence of
activation of the actuator 30 and/or initiator 110 depends to a
large extent on the design of the vehicle and to the size of the
passenger compartment. As an example, consider a frame or other
support structure of a particular vehicle which tends to absorb
less of the energy of a crash thereby transmitting more of same to
the occupant. In this situation, the more aggressive inflation rate
of Curve A may be called for. If the vehicle is such that it
absorbs more of the crash energy, a less aggressive inflation rate
such as Curve B would initially provide for the gradual envelopment
of the passenger. It can be seen, however, that based upon the
graphs of FIG. 11, that maximum air bag inflation is achieved at
approximately the same point whether or not the inflation procedure
is that for Curve A or Curve B.
In some situations it has been found that it is desirable to in
fact delay activation of the initiator 110 for a period up to and
perhaps exceeding 25 milliseconds. It can be appreciated that if
the inflator 10 of FIG. 1 is utilized, a significant amount of
cold, stored inflation gas will have left the pressure vessel 20
during this extended time delay period. FIG. 12 illustrates an
alternate embodiment of the present invention which illustrates an
inflator 300 suited to an inflation regime requiring extended time
delay activation periods. FIG. 12 illustrates the left hand portion
of such inflator 300. It should be appreciated that the right hand
portion is identical to that of FIG. 1. Inflator 300 comprises a
generator housing assembly 80', including a second manifold
assembly 304 welded to a sleeve end 28' at a circumferential weld
joint 305 to the sleeve 22'. The second manifold assembly 304 is
cylindrically shaped, terminating at a recessed end 306, having a
sharp edge opening 308. The end 306 supports a second burst disk
310. Positioned within the second manifold assembly 304 is the
generator housing 82, comprising the propellant 100, initiator 110,
etc. It should be appreciated that the burst disk 90, previously
used to enclose the opening 88 of the housing 82, has been removed.
An optional screen such as 312, similar to screen 64, may be
positioned across the opening 308. The manifold assembly 304
further includes a second set of gas flow orifices 320a and b,
disposed in a generally thrust neutral condition. Positioned about
the sleeve 22' is the diffuser 130 discussed above. In this
embodiment of the invention the flow orifices 320a and 320b are
sized to be larger than the flow orifices 70, fabricated within the
manifold 50. More particularly, the flow areas may have a ratio of
three to one. As an example, the total flow area of the orifices
70a and 70b may be approximately 0.32 square centimeters (0.05
square inches) wherein the total flow area of the orifices 320a and
320b may be approximately 0.97 square centimeters (0.15 square
inches). In response to a signal indicative of a crash situation,
the actuator 40 would be activated thereby opening the burst disk
62 causing a cold inflation of the air bag as the stored inflation
gases exit the orifices 70a and 70b, resulting in the reduced slope
portion of Curve C, FIG. 11. Thereafter, the initiator 110 is
activated causing the propellant 100 to burn away the second burst
disk 310, thereby creating a second flow path for the remaining
stored gas to exit the pressure vessel Upon removal of the burst
disk 310, the remaining stored gas exits the pressure vessel
through the opening 308, the optional screen 312 and then exits
through the larger orifices 320a and 320b, thereby increasing the
rate at which the stored gases exit the pressure vessel which
results in the increased slope portion of Curve C. As the inflation
gases exit the opening 308 they pass directly across the heat
generated by the propellant, thereby increasing the volume of same
as it exits the pressure vessel and flows into the air bag or
cushion.
FIG. 13 illustrates a further alternate embodiment of the invention
having a single pyrotechnic element such as the initiator 104. The
structure of this inflator 350 builds upon the alternate embodiment
shown in FIG. 12. More specifically, the left hand portion of this
inflator 350 is identical to that of FIG. 12. The sleeve portion
302 of the pressure vessel terminates at its right hand side in an
arcuately or perhaps spherically shaped surface 354. Attached to
the end 352 is a retaining member such as the cup-like structure
356 welded thereto. The ends 358 of this structure 356 include the
tabs such as 156 which, as previously mentioned, extend from the
actuator housing 32 for attachment to the diffuser end 132. A fill
tube 360 is provided in the end 352 for filling the pressure vessel
with inert inflation gas. Upon activation of the initiator 110, the
burst disk 310 is opened, thereby permitting heated inflation gas
to exit the orifices 320a and b. The resulting inflation curve of
this single pyrotechnic unit will essentially follow that of Curve
A of FIG. 11
Many changes and modifications in the above described embodiment of
the invention can, of course, be carried out without departing from
the scope thereof. Accordingly, that scope is intended to be
limited only by the scope of the appended claims.
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